In a seatbelt device equipped in a vehicle, there is provided a buckle device equipped with a tongue plate movably fitted on the middle of a webbing, and a buckle body through which the insertion and release of tongue plate is implemented. The buckle device is provided with a lock member for controlling the locking and unlocking of a lock bar for holding a lock position of the tongue plate so as to prevent the tongue plate from being released from the buckle body in case of an emergency of a vehicle such as a vehicle collision and so forth, wherein although the lock bar is normally kept at the lock position, when an operator releases the seatbelt, the lock member is rotated toward an unlock position, thereby causing the tongue plate to be released from the buckle body.
A buckle device disclosed in JP 6-66311 U (Patent Document 1) is provided with, as a fundamental structure, a buckle body, a hook member which is swingably supported by the buckle body and switchable to an engaged state or a disengaged state relative to a tongue plate, a lock pin which is supported by the buckle body and movable between a first position for holding the hook member in an engaged state and a second position where the hook member is released from the engaged state, a release button which is urged by a coil spring in the direction to pull out the tongue plate, and so forth.
Further, in the buckle device disclosed in this publication, a lock lever is rotatably pivotally supported in close proximity to the lock pin so as to make preparation in case of providing for drawing the buckle body toward a tightening side by a pretensioner so as to tighten the webbing in case of an emergency of a vehicle. At the time of insertion of the tongue plate, the lock lever is rotated and urged by a rotation urge member toward the lock position so as to cause the lock pin to be moved to the first position to hold the lock pin, while at the time of release of the tongue plate, the lock lever is forcibly rotated toward the unlock position so as to allow the lock pin to be moved to the second position.
Still further, at a position close to the lock lever, there is provided a sheet-like inertial body which is movably guided and supported in the direction to be moved to or away from the lock lever, and always urged by a spring member in the direction to be moved away from the lock lever. When the buckle body is stopped suddenly after it is drawn toward a webbing tightening side by the pretensioner which is operated in case of an emergency of a vehicle, the inertial body receives an inertial force at the lock lever side to be moved against an urging force of the spring member, thereby making contact with the lock lever to restrain the lock lever from being rotated toward the unlock position.
That is, the lock pin causes the lock lever to be rotated toward the unlock position, so that the hook member is rendered in engagement release, thereby preventing the tongue plate from being released from the buckle body.
Meanwhile, a buckle device disclosed in JP 4-58963 B (Patent Document 2) is provided with a lock mechanism capable of preventing the release of engagement of a latch member in addition to a latch member capable of engaging with and releasing from a tongue plate, an operation member for operating the release of engagement of the latch member, a lock member which is moved to a release position while interlocking with the operation of the operation member, thereby implementing the release of engagement of the latch member, and so forth. In this lock mechanism, there is provided a movement restraint member which is rotatably pivotally supported by the operation member and a part of which is intervened in a movement area of the lock member, wherein as a part of the rotating movement restraint member is present in the movement area at the time of generation of an impact, a moving lock member is butted against the movement restraint member to prevent the lock member from moving up to the release position.
In the buckle device disclosed in JP 6-66311 U (Patent Document 1), although the inertial body is moved to the lock lever side at the time of sudden stop of the buckle body, since the inertial force acting on the lock pin functions entirely as a force to cause the lock pin to be moved to the second position, there is a possibility that the lock pin is moved to the second position at very high speed.
That is, since there is a possibility that the lock lever is moved to the unlock position at very high speed, the inertial body which starts movement since the time of sudden stop of the buckle body does not normally make contact with the lock lever, resulting in arising a high possibility of not restraining the rotation of the lock lever toward the unlock position.
And also, there is a possibility that, although the lock lever pushes the lock pin to the first position at the time of insertion of the tongue plate, an oblique part of the rotating lock lever makes contact with the lock pin to transmit a force to the lock pin, resulting in failure of smooth implementation of the inserting operation of the tongue lever, and so forth. Further, since the lock lever, the inertia body, and urge members each urging these members must be provided, respectively, in order not to release the tongue plate from the buckle body owing to the operation of the pretensioner, the number of parts is increased to make the structure complex, and the assembly of the buckle device becomes complex, resulting in the disadvantage in a manufacturing cost.
Meanwhile, according to the buckle device disclosed in JP 4-58963 B (Patent Document 2), although a part of the movement restraint member is intervened in the movement trajectory of the lock member in a normal state, the movement restraint member is also rotated owing to the vehicle collision and so forth, resulting in arising a possibility that the lock member is not butted against the movement restraint member while the part of the movement restraint member is present in the movement area of the lock member, whereupon if such a case occurs, the latch member is released in engagement, so that the tongue plate is released.
Accordingly, in the buckle device provided with the tongue plate and the buckle body, there is proposed a buckle device as disclosed in JP 2001-46117 A (Patent Document 3) so as to reliably prevent the tongue plate from being released from the buckle body in case of an emergency of a vehicle, realize the smooth and reliable inserting and releasing operation of the tongue plate in a normal state, and simplify a structure to cause the tongue plate not to release from the buckle body in case of an emergency of the vehicle.
The present invention aims to add the improvement to the structure of the buckle device disclosed in the Patent Document 3, thereby solving the problem thereof more reliably.
The first object of the present invention is not to impair a normal working performance while a tongue plate is not released from a buckle body even at the time of operation of a pretensioner.
The second object is to assure the releasing operation by causing a lock bar to be moved merely in the direction to unlock a lock member after a second engagement part of the lock member is butted against the lock bar at the time of operation of a pretensioner and so forth.
The third object is to cause the lock member to generate a rotative force in the direction to hold a lock position so that the lock member holds the lock position for a period from the time when the lock member is moved away from the lock bar until the time when a third engagement part of the lock member is butted against a release button, which is caused by the sudden stop of drawing after the operation of the pretensioner.